78 



sufficiënt — just think of the colourless sponges in darkness with 

 an import just as large (but with a much smaller multiplication 

 and a much greater mortality) — also a rather considerable 

 multiplication is required and low mortality. 



What about this multiplication and this mortality of the green 

 algae in a sponge, compared with those phenomena in algae free 

 in the water? Is in light the intensity of multipUcation in a 

 sponge larger^ the same or smaller than in water? 



For this see Table 10, to which I have already referred 

 several times. In this table there is given every time in column 1 

 the intensity of multiplication of the green algae for a sponge in 

 the light (and in the dark) and for a culture in water from the 

 conduit or from the lake in light (and in darkness). From that 

 we see that in most experiments the intensity in the water is 

 ever so much larger than in the sponge ; in the latter it is 

 generally below 15, in water it amounts to 20 — 35 ! 



Let us, for the present, not ask how that phenomenon in caused ; 

 at any rate it goes without any doubt for these experiments. 

 No-w what ahout the total nmnber of green algae when cultivated 

 in light in sponge and in water? See Table 10, column 3. That 

 number proves, notwithstanding the much larger intensity of mul- 

 tiplication in water, in general in water less increased than in 

 the sponge. So it cannot be otherwise than that the algae, which 

 have much more multiplied in water, must also have been more 

 destroyed there, in some way or other, than in the sponge. (With 

 all these experiments the factors of import, export, reduction and 

 of growth were excluded as much as possible). So all things 

 together, the algae in the light are in more favoiirahle conditions 

 in the sponge than in the water; really the sponge must protect 

 its algae against destruction '), 



This fact must also inevitably appear, when we notice that, 

 according to Table 8, entirely colourless sponges with only few 



1) To get this result puiely, we must compare the algae with equal begin-concen- 

 tiation in sponge tissue and in water from conduit, of couise, after they have been 

 cultivated for the same time and at the same temperature. Then consider what is stated 

 in the following pages (p. 82 — 83). 



